In this publication, the following abbreviations are used.    CBS Committed Burst Size (greatest permitted burst size [bit]), when exceeding the committed information flow,    CIR Committed Information Rate (greatest permitted mean traffic speed [bit/s]),    CoS Class of Service    FIFO First In, First Out discipline,    MP Measuring Point, in which the speed characteristics of the traffic flow are measured (e.g., mean traffic speed, momentary traffic speed, bust size),    PIR Peak Information Rate (greatest permitted momentary traffic speed [bit/s]),    PKS Packet size in bits,    V1, V2, . . . Traffic flow 1, 2, . . . ,    VTS The earliest moment in time, after which the next packet representing a specific traffic flow may be forwarded, in order that not even one rule set for a speed property of the traffic flow in question will be broken (Valid Time to Send),    VTS_CIR The earliest moment in time, after which the next packet may be forwarded, in order that the greatest permitted mean speed and/or the greatest permitted burst size will not be exceeded,    VTS_PIR The earliest moment in time, after which the next packet may be forwarded, in order that the greatest permitted momentary speed will not be exceeded.
In packet-switched telecommunications systems, it is often advantageous if the packets being transmitted are classified in different service classes (CoS) according, on the one hand, to the requirements of the applications using the telecommunications service and, on the other, to the kind of service-quality agreements that the telecommunications service provider (Service Provider) has made with its customers. For example, in a telephone application (Voice over Internet), it is essential for the data-transfer delay and the variation of the delay to remain below the permitted limit values. The permitted limit values are often defined in a service-quality agreement. However, when downloading www pages, for example, the data-transfer delay and its variation are significantly less critical quantities.
It is often wished to monitor and limit the speed properties of a traffic flow formed from packets to be transferred. Such a situation occurs, for example, if it is wished to reserve a specific portion of the data-transmission capacity of a transfer link for a specific customer, so that the traffic of the customer in question will not be permitted to exceed the transmission capacity reserved for him. The traffic flow being examined thus consists of packets representing the traffic of the customer in question, which can represent differ service classes. In other words, a virtual transfer link is formed to the customer in question, the transmission capacity of which is part of the capacity of the physical transfer link used for the implementation. A speed property can refer to, for example, the mean speed of the traffic (CIR), the burst size (CBS), by which the mean speed can be momentarily exceeded, or the momentary speed (PIR). Taken more generally, the traffic flow can consist of, for example, packets to be routed to a specific transfer link, packets with a specific source address and sent by a specific end user, or packets that belong to a specific class of service (CoS) and are to be routed to a specific transfer link. In the rest of this publication, a system, which can be used to monitor and limit the speed properties of a traffic flow, will be referred to as a ‘shaper’ and the operation, in which the speed properties of a traffic flow are monitored and limited, will be referred to as ‘shaping’.
The following examines a system, to which two traffic flows V1 and V2 arrive. The traffic flow V1 arriving in the system represents delay-critical traffic (e.g., Voice over Internet), for which a greatest permitted delay and delay variation have been defined. The traffic flow V2 arriving in the system represents traffic that is considerably less delay-critical than that of flow V1. The traffic flows V1 and V2 are multiplexed to a common transfer link S leaving the system. Multiplexing is performed on the basis of priority, in such a way that the packets representing the traffic flow V1 are forwarded with a higher priority than the packets representing the traffic flow V2, because traffic flow V1 represents delay-critical traffic. It is wished to monitor and limit the speed properties of the aggregate flow A being transmitted to the transfer link S.